To date, acrylic tackifiers, and rubber-based tackifiers mainly containing rubbers such as natural rubber and polyisobutylene, are primarily used as tackifiers for the adhesive layer of a surface protection film. Methods involving a roll, spray, or the like to apply a tackifier solution in which a tackifier is dissolved in a solvent are used as methods for applying such a tackifier to a predetermined support film. Although such methods are capable of forming the tackifier layer uniformly and thinly and are thus advantageous, the use of a solvent is not preferable from the viewpoint of air pollution, fire, safety and health during production, economy, and so on.
On the other hand, as a production technique for a hot-melt-type surface protection film for which solvents are not used, a technique that produces a laminate of a tackifier layer and a support film by coextrusion is known, and concerning tackifiers as well, various hot-melt tackifiers have been developed (see, for example, Patent Literature 1).
As a tackifier having excellent tack strength, a tacky composition has been proposed that is composed of an epoxy-modified hydrogenated block copolymer composed of a block mainly including a vinyl aromatic compound and a block mainly including a conjugated diene, wherein some double bonds of conjugated diene portions are hydrogenated, and the rest of the double bonds are partially epoxidized (see, for example, Patent Literature 2).
Furthermore, a coextruded film has been proposed in which a tackifier layer is made of a copolymer mainly including ethylene such as EVA and having a high level of affinity to olefinic resin films in the case of using as a support film an olefinic resin film that is a typical material to which adhesives are unlikely to adhere (see, for example, Patent Literature 3).